Re: starship-design: We need to get on the same (pellet) track first

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

Timothy van der Linden wrote:
>Hello Isaac,
[...about black hole "drives"...]
>>The second, and more plausible idea, is that of using a black hole
>>to produce usable antimatter.  With sufficiently massive construction
[...]
>I wonder though what momentum per unit of mass both designs would give you.
>The problem with using a blackhole is likely has to be too heavy to produce
>a usable amount of energy. As a result the "engine" would be much heavier
>than the fuel.

Actually, black holes produce _more_ energy the smaller they are.
In fact, if you don't keep feeding it, it will explosively evaporate
away.  Playing around with small black holes makes letting Calvin
play with a flame thrower indoors look positively safe.

As for the potential for the latter concept, it all really depends
upon how good an antimatter powered rocket you can make.  Antimatter
rockets look ideal for interstellar travel, assuming you can get a
lot of it.

>>>You suggest the acceleration of a pellet happens almost instantaniously by
>>>some plasma expansion. I wonder, won't the launcer blow apart?

>>I didn't specify, but the plasma pusher is pushed forward using
>>a rail gun design.  Easier to get high muzzle velocities this way
>>than with other methods.  Compared to a TNT detonation, this is
>>a gentle push.

>True, but even if it is a gentle push compared to a TNT detonation, it
>likely is still a big bang. What do you suggest is the mass of the pellet
>you want to accelerate?

Very small.  Anyway, I'm no expert on electromagnetic railgun designs,
but plenty of real scientists doing real research on actual railguns
are, and some of them even have web pages.  Search Yahoo! with
"electromagnetic railgun".  There are a lot of cool things out there.

Particularly pertinent to this discussion is research into hydrogen
pellet accelerators for magnetic fusion reactor fueling, since these
same pellets would be ideal for the fusion ramjet I'm proposing.
Muzzle velocities of over 3km/s have been demonstrated, but I
suggest thinking in terms of only 1km/s or so because the fuel packets
will ideally have a lightweight railgun with a limited power supply
(on board fission and/or collection panels for ship based beamed
power).

>>>>This ramjet isn't supposed to scrounge around for interstellar
>>>>hydrogen, so its diameter is determined by how accurate the
>>>>pellet tracks can be laid and followed.

>>>To Kelly you wrote "TV tubes don't have to be many times longer than they
>>>are wide", you already noted that protons need 1000 times more energy.
>>>I think that the amount of protons/electrons will make a difference too.

>>You're right, it does, because the curved paths of the affected
>>particles are essentially induced currents which induce a magnetic
>>field opposing the original one.  However, it's not as simple as
>>requiring twice as much field to handle twice as many particles.
>>In a TV tube, the induced magnetic fields from the moving electrons
>>are, of course, negligible.  I confess I haven't done the math
>>to come up with how strong the induced magnetic fields are for
>>a DT pellet.

>It might be interesting to do some rough calculations. If we'd catch 1 kg of
>hydrogen ions that means 6.2E26 ions and a current of 1E8 Ampere.
>That current alone would generate non trivial magnetic fields. On the other
>hand we would have a similar amount of electrons that go the same direction
>(however likely along the outside of the ship).

Your analysis is flawed because the electrons would travel along with
the ions.  It would be very nice if we could somehow convince the
electrons and nuclei to somehow part from each other, because then
electric fields could be used to manipulate them as well as magnetic
fields.

However, they're rather stuck on each other because of their
opposing electric charge.

Anyway, the sort of pulsed fusion I'm proposing is similar to
magnetic target fusion, which requires starting densities of
10^18 nuclei per cm^3.  The specifics of the plasmatizing of
the pellet would determine what mass of pellet is needed.
I'm not familiar enough with the factors involved to make a
good assessment of that part.

>>>A more practical question: How are the superconducting magnets kept from
>>>blowing up? The charged particles that fly trough the magnets will create a
>>>magnetic flux. Normally as long as the particle flies trough without
>>>velocity gain, the superconducting magnets will have the same current before
>>>and after the particle flew trough. But in the ramjet design the particles
>>>will exit faster than they arrived and thus will leave a non-zero flux.
>>>I do know little about how superconductors are given a current and a
>>>magnetic field, so the above question is more likely a result of not knowing
>>>then of doubting the design.

>>The superconductors resist any change in the magnetic field, which
>>is one of the ways they are so different from normal conductors.

>If I understand correctly, the way that they resist that change in magnetic
>field is by changing the current inside the superconductor.
>In the situation explained above, the current would rise more and more until
>the current would become too high and break down the special properties of
>the superconductor.

Yes, but since the magnetic field they are resisting is only momentary,
so is the opposing electric current.  It doesn't build up.
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
 __|_)o(_|__
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi